Conventionally, there are security systems for children which pre-set areas where they are permitted to travel, such as school zones, and transmit notifications of the children's current positions and the like when they move outside the permitted areas, since the situation is recognized as unusual (Refer to Patent Reference 1). With such systems, when a child moves outside the pre-set area such as a school zone, the possibility of being kidnapped, for example, is notified to those who care for the child such as parents, thus making it possible for crimes to be promptly notified.
Also, there are devices, made up of a base unit and a handset, for detecting a distance between these terminals, and notify, through a warning, the base unit or the handset that they have separated from each other when the distance becomes a predetermined distance or longer (Refer to Patent Reference 2). With these devices, in a situation where parents are letting their children to play in a park, for instance, it is possible to prevent the children from running out into a road, for example, by providing a notification to the terminals when they have separated from each other by the predetermined distance.    Patent Reference 1: Japanese Unexamined Patent Application Publication No. 2003-174396    Patent Reference 2: Japanese Unexamined Patent Application Publication No. 2003-109147